This invention relates to a novel stem-sealing method for use in assembling electron tubes including an improved method for removing the excess glass or cullet from the sealing machine.
Stem sealing is a widely-used process in which a glass stem is sealed into the glass neck of an electron tube. The stem is a wafer-shaped piece of glass with the exhaust tubulation extending from one side, the stem leads sealed into and extending therethrough, and the electron gun mounted on the stem leads on the other side. Stem sealing is usually conducted on an automated machine comprising a rotatable turret having a plurality of rotatable supporting means, each including a mount pin for supporting a stem and an envelope holder for supporting an envelope in controlled positions with respect to one another. The envelope and stem are loaded onto the supporting means at a loading station. Then, the turret rotates intermittently from one station to the next until the stem is heat sealed into the neck and the confronting glass, which has been melted to make the seal, is solidified and annealed.
Prior to sealing, the neck, which usually is tubular, is much longer than necessary. During the sealing operation, when the glass is molten, the excess glass is cut off with a sharp flame, and the molten edge solidifies and sticks to and around the mount pin. The operator, upon unloading the sealed envelope, smashes the excess glass or cullet from the mount pin, permitting the fragments to fall in and around a bin adjacent the unloading station. The practice of smashing the cullet is undesirable because it results in poor housekeeping around the sealing machine. Also, the glass fragments may cause injuries to nearby personnel. In addition, the practice of smashing the cullet generates very fine glass particles which become airborne and drift through the factory settling randomly on work surfaces and surfaces of the product. For example, where the factory is making aperture-mask-type color picture tubes, glass particles frequently settle on in-process aperture masks. When these masks are assembled into tubes, the presence of these glass particles may cause the finished tubes to be defective.